1. Field of the Invention
The present invention concerns a method of detecting relief contours in digital images representing an aerial or satellite view of the ground. An application of the method constructs accurate crest lines on a digital elevation map.
2. Description of the Prior Art
Contour detection is a standard problem in image analysis and there are many techniques available. However, these prior art techniques do not address themselves to the nature of the contours and in particular cannot distinguish contours representing relief discontinuities (typically crest lines) from texture contours (for example the boundary between a cultivated field and a forest).
There are many applications of a method of distinguishing relief contours and texture contours. One example is detecting man-made structures in aerial or satellite images. These structures are generally characterized in that they have sharp edges (i.e. crest lines) which can be located to detect the contours of the structure. The prior art methods are evidently insufficient to solve this kind of problem.
The present invention alleviates this insufficiency and proposes a method of analyzing images capable of detecting only contours marking crest lines, exclusively.
For this the method of the invention requires two calibrated stereoscopic images of the same terrain, i.e. two images of the same terrain taken with different but known imaging parameters.